188 



nearly the direction of the line drawn to the nearest point of the 

 coast.*' 



The variation in the epoch of the maximum intensity of the current, 

 at different places, is also in accordance with the same principles ; that 

 epoch being earliest in islands, or places nearly encompassed by sea, and 

 latest in the interior of the great continents. Thus it occurs at noon 

 at St. Helena, and in the southern parts of the peninsulas of Hindostan 

 and the Malaya ; while it takes place at 2 p. m. at Catherinburg and Bar- 

 naoiil, in the interior of Siberia. This accords with the laws of the sun's 

 calorific action. 



It will be seen, upon an inspection of the diurnal curves of the 

 Earth-currents (Trans. E-oyal Irish Academy, vol. xxiv.), that at most of 

 the northern stations, as well as at Hobarton in the southern, the 

 easterly currents being greater than the westerly. I believe this effect 

 to be due to the disturhance-currents, which (as I have already shown) 

 have an easterly tendency. This preponderance of the easterly currents, 

 however, is found to be greater at places — such as Greenwich, Dublin, 

 Makerstoun, and Toronto — which are near an eastern coast, than at 

 those places — such as Petersburg, Catherinburg, and Barnaoul — which 

 are in the interior of the continent. The results, therefore, so far con- 

 firm the supposition above made. 



There are, unfortunately, very few places situated near the ivestern 

 shore of a great continent, at which continued observations of the 

 two magnetic elements have been made. I know of none, excepting 

 Sitka, on the western coast of J^orth America. The results at this 

 station, however, confirm the view above stated, — the ivesterly currents 

 being there greater than the easterly. 



There are probably many other circumstances in the configuration 

 and structure of the earth's surface which influence the direction and 

 magnitude of the currents ; but I incline to think that the principal one 

 is that above stated, viz. the distribution of land and water in the vici- 

 nity of the place of observation. It may be, also, that this cause is suffi- 

 cient to account for some of the peculiarities in theTorm of the diurnal 

 curve noticed in my former communication, and there referred to other 

 causes. Thus, it is not improbable that the persistent direction of the 

 current at Munich, there referred to the influence of a mountain range, 

 may be, in fact, the result of the proximity of the Adriatic Gulf, which 

 lies nearly in the direction of the persistent current. 



* These additional results oblige me to abandon the conclusion formerly derived 

 from a more limited induction, that the direction of the current of greatest intensity- 

 is connected with the magnetic meridian of the place. From the facts which we 

 now possess, it would appear that the currents afl'ect a meridional direction in the 

 higher latitudes, while they are nearly parallel to the equator within the tropics. This 

 will be seen in a striking manrar by comparing the directions of the maximum currents 

 in India, above given, with those of the Russian stations in the northern part of the Asiatic 

 Continent. 



